This invention relates to an acoustic device comprising at least one speaker installed in a headrest provided on the top of a seat.
Recently, a variety of acoustic devices each comprising a speaker installed in a headrest provided on the top of a seat have been proposed and commercialized. For instance, Japanese Published Utility Model Application No. 16409/1978 has disclosed an acoustic device in which a speaker is installed on one end of a flexible arm, the other end of which is secured to the arm of a seat or a headrest provided on a seat so that a person sitting on the chair can appreciate music more comfortably than if the person had worn a head receiver such as a headphone. In an acoustic device disclosed in Japanese Published Utility Model Application No. 6059/1984, similarly to the above-described acoustic device, a speaker is set in the vicinity of the listener's ear, and a so-called "driver unit" is installed on the seat, so that the listener can feel extremely low frequency sounds through his body.
In an acoustic device disclosed by Japanese Published Utility Model Application No. 133188/1982, a bracket is secured to a post supporting a headrest, and a speaker is ccnnected to the bracket so as to be positioned beside the headrest, so that the speaker can be directed upwardly or downwardly, or to the right or left. In an acoustic device disclosed by Japanese Published Utility Model Application No. 188486/1982, one end of a pipe supporting a headrest is connected to a chamber behind a loudspeaker, and the other end is passed through the inside of a seat and opened inside the seat, so that low frequency sounds are made significant by a so-called "bass-reflex effect".
Japanese Published Utility Model Application No. 119282/1983 has disclosed a acoustic device in which a speaker is buried in the top of a seat.
However, the above-described acoustic devices disclosed by Japanese Published Utility Model Application Nos. 16409/1978 and 6059/1984 are disadvantageous in that the speaker is located very close to the listener's ear, decreases the listener's field of vision, and may strike the listener if there is an accident. Accordingly, these conventional acoustic devices cannot be used in automobiles or other vehicles.
In the acoustic devices disclosed by Japanese Published Utility Model Application Nos. 133188/1982 and 188486/1982, the speaker is arranged beside the headrest (or obliquely backwards of the listener's ear), that the listener's field of vision is wide, and the danger of accidental injury is lower compared with the two above-mentioned conventional acoustic devices when used in a vehicle. However, there is still the disadvantage that, since the speakers face the listener (or driver), the headrest is wider by the diameters of the right and left loudspeakers, so that the dead angle toward the rear of the automobile is increased as much.
In the acoustic device disclosed in Japanese Published Model Application No. 119282/1983, since the speaker is buried in the top of the seat, the field of vision of the listener will not be obstructed and the dead angle will not be increased. However, the acoustic device is disadvantageous in that the speaker faces upwardly. Therefore, because of the directional pattern of the loudspeaker, and more specifically because of the relationship between the direction of the main axis of the speaker and the position of the listener's ear, it is difficult to obtain a flat sound transmission characteristic. Furthermore, when the listener's head is moved, frequency response varies greatly because of the directional pattern.